There are many applications which require not only detecting objects within a field of view, but also determining the distance to each detected object. Such applications include power line detection to ensure the safety of moving helicopters, runway light detection to assist jets during landing, etc. Outside of stereographic imaging methods, the usual optical imaging methods do not allow rapid and precise determination of the distance to objects captured in an image.
Stereographic imaging requires capturing at least two images of the same object from different angles of view. This requirement leads to the following difficulties:                at least two image capture devices must be installed in parallel, with precisely defined positions relative to each other;        the images must be captured at the same moment if the captured object is moving; and        image correlation software is required for comparing the positions of the same object in the images captured separately by the two devices.        
Planar optical components are known, in which the transmittances vary as a function of two coordinates inside the plane of each component, and have two-dimensional Fourier transforms which consist of peaks located on a circle of a determined radius. Such components are said to be continuously self-imaging and are described in the article entitled “Exact solutions for nondiffracting beams. I. The scalar theory,” J. Durnin, Journal of the Optical Society of America A, Vol. 4, pp. 651-654, 1987, and in the article which defines continuously self-imaging gratings and which is entitled “Generation of achromatic and propagation-invariant spot array by use of continuously self-imaging gratings,” N. Guérineau et al., Optics Letter, Vol. 26, pp. 411-413, 2001.
In addition, the presentation by Piponnier et al. which is entitled “Analysis and development of non-diffracting arrays for the design of advanced imaging systems,” Journées scientifiques de l'Ecole Doctorale Ondes & Matiéres (EDOM), 7-8 Mar. 2011, proposes associating such a continuously self-imaging component with an image sensor for applications involving detection, identification, or accurate location determination for simple objects.
An object of the present invention is therefore to propose a new method of range imaging which does not have the disadvantages cited above for the stereographic methods.
In particular, one object of the invention is to determine the respective distances to multiple objects contained within a field of view, based on a single image captured.
Another object of the invention is to determine simply the distances to the objects without requiring significant computational capacity.